Researchers report overnight cycle of water movement in trees

A high-precision, three-dimensional survey of 21 different species of trees has revealed an as-yet unknown cycle of subtle canopy movement during the night, reports Phys.org.

Such ‘sleep cycles’ differed from one species to another. Detection of anomalies in overnight movement could become a future diagnostic tool to reveal stress or disease in crops.

One of the most important processes sustaining life on Earth is the transport of water from the ground and into the leaves, where photosynthesis occurs. The process has fascinated scientists for centuries, and is still debated in plant physiology. Scientists generally agree that water transport is driven by light, and consequently occurs in 24-hour cycles.

Overnight movement of leaves is well known among tree species of the legume family, but it was only recently discovered that some other trees also lower their branches by up to 10 centimeters at night and then back in the morning. These branch movements are slow and subtle, and are difficult to identify with the naked eye at night.

However, terrestrial laser scanning, a 3-D surveying technique developed for precision mapping of buildings, makes it possible to measure the exact position of branches and leaves. This technique was recently used to demonstrate movements in the branches of birch trees under field conditions.

When a team of researchers from Denmark and Hungary repeated the experiment by bringing 22 individual tree and shrub species together and scanning them overnight under strictly controlled conditions, they were surprised: “We detected a previously unknown periodic movement of up to one centimeter in cycles of two to six hours. The movement has to be connected to variations in water pressure within the plants, and this effectively means that the tree is pumping. Water transport is not just a steady-state flow, as we previously assumed,” said postdoc András Zlinszky at Aarhus University, department of Ecoinformatics & Biodiversity.

Pulses of movement

All the trees showed some kind of branch or leaf movement of a few centimeters during the experiment. However, the overnight 12-hour cycle of lowering and returning to the starting position was only observed in seven of the species studied. The results revealed that some trees have “sleep periods” shorter or longer than 12 hours, and others show slow continuous movement in one direction, probably because of disease or senescence.

The most striking finding was that all the studied plants displayed pulses of minute periodic movement overnight. This was particularly striking in the magnolia tree, which completed three full cycles of up-and-down branch or leaf movement over one night. Although the crown displacement measured was only about 1 centimeter, the scientists are confident that this is not a measurement error.

Short-term plant movements are caused by changes in water pressure within tissues. It is generally assumed that water transport in trees takes place as a steady-state process with no variations faster than the day and night cycle. The new findings suggest that short-term change in water transport and tissue pressure is widespread.

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I glad to see researchers have discovered another thing that good farmers/gardeners have known for eons. Plants do “sleep” and they “breath” oxygen, drink water. Carbon Dioxide is fertilizer that they use with water to make carbohydrates in sunlight. Carbohydrates that they “burn” at night to keep warm…pg

All plants pump. Water does not defy gravity without work. This work in plants was thought to be limited to capillary action, a property of the polarized water molecule where its attraction to the surrounding tube is greater than its cohesive attraction. Think meniscus.

What this study shows, is that at least Magnolia has the ability to control the pump. Amazing.

They all have the ability to ‘control the pump’; up to a point. Most times the pump is on ‘auto’, internal osmotic pressure.

In low relative humidity and in direct strong sunlight, a small tree will move a large quantity of water for transpiration. If water becomes scarce, it wilts, by several inches, reducing its area exposed to sunlight. Loading the water supply with chemicals hinders osmosis; it wilts more, and possibly permanently.

The paper is paywalled; $42 for one hr on-line read. Makes it dubious value for money.

I retired from engineering, I’d like to think, but not from my agrarian roots. I have been seeing similar. While it is research I get the feeling of a widening disconnect, where sight of the woods is being lost. For the trees? Or as it appears, too connected to technology and the desk and laptop. Agriculture is far more complex than that.